Take Real Analysis, but take it at a time when it will be your highest priority. Getting an A in Real Analysis will be a big help in getting you into top programs, and getting you funding.

Think about learning a programming language. Python is good for many tasks.

Work for 2 years after undergrad and before graduate school, preferably at a job that improves your data analysis or theoretical modeling skills.

How should you decide which programs to apply to?

Talk to your academic advisor, thesis advisor, and bosses at work. (You ARE working for two years between undergrad and grad school, yes?) Aside from you, they know you and your potential best.

Know that there are several types of degrees that can get you the same jobs. A Public Policy PhD is generally thought of as less prestigious than an Econ PhD from the same school. For example, a PhD from Harvard's Kennedy school is less fancy than a PhD from Harvard Econ. The same is true of Agricultural or Applied Economics degrees. However, a PP PhD from Harvard out ranks an Econ PhD from Michigan and depending on your package, you may have a better shot at a PP/Ag/Applied program at a fancier school than an Econ PhD from a less fancy school. Fancier schools tend to have more money to give you grants and more name recognition to get you job interviews. So for your applications, you should think of a portfolio strategy in which you apply to some Econ PhDs and some PP/Ag/Applied PhDs.

Start at the top of the rankings of schools. Various rankings can be found here: https://www.aeaweb.org/resources/students/grad-prep/program-rankings

Decide what fields you might be interested in pursuing and make separate lists of schools that are good in those fields. The top 5-7 are good at everything. After that, not all schools are good at all things. These rankings by field are old but not a bad place to start: http://econphd.econwiki.com/rankings.htm

For the top 30 or so schools on your list, visit their webpage and find out what programs they offer: Econ, Public Policy, Ag/Applied Econ. PP/Ag/Applied programs that require you to take classes with Econ PhD students are usually better than those that do their own thing. Look particularly at the methods classes. Is it real econometrics or is it "methods"? Look at the professors who teach in those programs. What are they good at? Are their recent working papers interesting to you? Are they publishing in good journals? Are they publishing regularly? You're looking for potential PhD advisors who are active but still have time to mentor you. Winnow your list to 20 or so.

Try to find the recent placements of each program on your list. Remember, you're looking for a job at the end of this, not just a PhD. Where are people being placed? Would you be interested in those jobs? Can you figure out how many do not get jobs when they graduate? Some schools post placement lists on their website. For others, a graduate program secretary will send you a list if you ask nicely. To determine the fraction of students who don't get jobs, or don't get jobs their first time out, look at this year's job market candidates (these are usually posted November-February). What is the average number of years the job market candidates have been in the program? Good programs graduate most students in 5-6 years.

This one is a bit of a reach, but try to find out what fraction of incoming PhD students are fully funded (meaning a tuition waiver and a living stipend), either through grants (preferably) or through RA jobs (next preferred) or TA jobs. (DO NOT TAKE OUT LOANS if you can possibly avoid it, particularly in your first year.) Again, a graduate program secretary might be willing to tell you.